Google Slides among other Alphabet products are tied to your Google account. Meaning many settings and language interfaces are mostly unified. Changing the language will inevitably affect other services that you used under the account.
But changing the interface language on Google Slides may be a good thing. For starters, it helps people understand the functions and features within the service without them relying on a translator service. And then, measurement units like cm/inch and Celcius/Fahrenheit will largely depend on the language settings too.
If you want to change Google Slides (and the entire Google account) language from English to your mother language, follow these steps.
1. Click your Google profile picture to reveal more menus. Then, select Manage your Google Account
2. On the search bar, find and select Language (because it’s easier this way).
3. Click the pencil icon to change the language.
4. Find your preferred language.
5. The language may contain diverse regions to choose from. Select your preferred region.
6. Launch or refresh the existing Google Slides page and enjoy the new language interface.
As the language and region affect some aspects of Google service, you may miss or discover new features after. For instance, many Google Slides templates are missing once I switched from English to Deutsch. However, each available template is translated nicely although existing documents don’t see any effect.